Vapor electric device cathode



May 26, 1953 l GI EW|N ETAL 2,640,171

VAPOR ELECTRIC DEVICE cATHoDE Filed oct. 25, 1951 Z0 1:/ gm

Patented May 26, 1953 TENT OFFICE (Cl. S13-178) 7 Claims.

This invention relates to cathode construction oli a vapor electricdevice and, more particularly, 'is a cathode of sponge type under thegeneral classification of solid cathodes, and also includes features ofnovelty in the method of fabrication thereof.

Sponge cathodes have been made of various materials and operate onthe'fact and-theory that the porous nature of 'the .sponge obtains acapillary action with respect to the mercury of` an ignitronto' keep a`copious supply thereof at the arc bearing surface of the sponge duringoperation; We have found that the metals of the platinum `group areexcellent materials for constituting the sponge portion of -the cathode,but thecost of Asuch materials is prohibitive for use inl commercialapplications.

The present invention accordingly is directed to a sponge cathodeconstruction enabling these desirable but costly metals to beeffectively used in email quantities.

Specifically., the invention has objectivesA of constructional featureslimiting the arc-striking surface of anycostly `rruetal as to size andthe total amount of this metal andiyet obtainthe benefits thereof tofullest extent necessary or desirable.

Other objects ofthe invention will appear to persons skilled yin the artto which itappertain's asthe description v'thereof proceeds, both bydirect recitation and by implication 'from the context.

Referring to the accompanying drawing, in which like numeralsi ofreference `indicate similar parts throughout the several Views.:

Fig. 1 is a vertical section of an essential portion of an ignitronwherein the present invention is included;

Fig. 2 is a cross-sectional View on line II--II oflig. 1;

Fig. 3 is a longitudinal sectional View `of a die arrangement forfabrication of the sponge cathde;

Fig. 4 is a detail section of a portion of the sponge cathode as formedby the dies; and

Fig. `5 is aldetail sectionsimilar to Fig. 4, showing the completedconstruction of the same portion of the sponge cathode.

In the specific embodiment of the invention and associated ignitronconstructicnillustrated in the drawing, but without limiting to detailsthereof, a sealed cylindrical casing Ill of steel cr other sturdymaterial is shown having a bottom I2 integral therewith and having, at adistance above said bottom, an anode I3 appropriately supported andinsulated from the casing as usual in the art. Between said` anode i3`and bottom 'I2 is anv ignitor I'4 here shown located axially' of thecontainer and directed toward and terminatingat its bottom in engagementwith a sponge cathode I5 located on said bottom wall I2. Said ignitormay be composed of materials as used Vfor i'gnitors of the prior art, ormay be of such other material or ymaterials adapting' it more especiallyto the present invention.

Said sponge cathode I5 preferably fits the container at its peripheryand frictlonally Aor 'otherwise is held permanently in fixed position.According to the present invention, the sponge portion of the spongecathode I5 is constructed essentially of two different materials, ofwhich one is used to take advantage of its relatively large intersticesbetween granules for providingl generous reservoir capacity, and also totake advantage of its characteristic of ainity, for and absorption ofmercury coming in contact therewith. Selection of the other material toconstitute the sponge portion of the cathode is for purpose of providingan `arc-striking surface highly resistant to erosion due to the 'arc andyet `of a character which will present a generous supply of mercury tothe surface thereof by capillarity, and also oi' a nature not readily`contaminated or poisoned during fabrication or during use. Morespecifically, the body portion I6 of the cathode is essentially ofsintered iron or other material having high absorptive afnity for thereconstructing `cathode fluid, such as the mercury above mentioned, andon said body is an arcstriking portion I'I of a character having theabove-recited advantages and preferably a material of the platinum groupof which both platinum and ruthenium are highly desirable examples. Inview of the high cost of these platinum group materials, however, thepreviously developed technique for arc-striking inserts in sponge bodiesis impracticable, and the construction by which approximately one to twograms of the precious metal for the size of ignitron disclosed below isrequired constitutes the essence of the present invention.

The arc-striking portion I'I comprises a disc less than half of thediameter of body portion le 'and of a thickness of substantially lilroproportion, so it is only a very small fraction of the thickness of thebody portion. It may further be defined as so thin that it would not bealone self-supporting and requires the body portion for support toremain intact. For instance, an ignitron having a three and one-halfinch diameter of cathode body and quarter inch thickness lof body, thearc striking portion would be portion .of the sponge cathode.

approximately an inch in diameter and have a thickness of approximatelytwo hundredths of an inc-h or less, and perhaps more vividly describedas paper thin. Its location is shown upon the upper surface of the bodyportion and coaxial thereto so as to be centrally contacted by theigni-tor and lower end of which presses against the top central regionof the said arcstriking portion.

The arc is limited to the top surface of the said arc-striking portionby a molybdenum or other refractory metal or insulating ring I8superposed at the peripheral margin thereof. Said ring has an inturnedange I9 engaging atwise on the said margin of the Yarcstriking portionand has appropriate retainers 20 for holding the ring in place. Theretainers may be variously constructed and in the presentl showingcomprise wires of iron, molybdenum or other suitable -material havingone end embedded in and held securely .by the sponge body and pro-'primarily by utilization of pressure laccomplis-hed by provision of ahollow die 2| the inside diameter of which is made to correspond, withcompensation for shrinkage, to the desired `diameter of the cathode bodyto Ibe formed. The bottom -end of this hollow die is closed by a lowerdie 22 having holes therein for placement of .the wires or otherretainers 20. Said lower die furthermore has a properly located socket23 for reception and ultimate compression of the platinum group metal toform the arc-striking An upper ydie 24 is depressible within the hollowdie with a movement toward the lower die for compressing the material,placed on the lower die, into cake form 'to comprise .the spongecat'hode.

In practice, the platinum group metal, in powder or granular form, isfirst introduced into socket 23 of the lower die and leveled 01T to theplane of the top of that die. As the socket is shallow, a very limitedamount of the multitudinous particles of the metal is required to ll it.Then the wires 20 are inserted into the lower die 22. Next, apredetermined volume of granular or otherwise prepared material ofmultitudinous particles or units, such as iron powder, is introducedinto the hollow die on top of the lower die and on top of the filledsocket, and surrounding the upwardly projecting ends of the wires orretainers 2U previously placed in the lower di-e. A pressure ofapproximately 8 tons per square inch is then applied by the upper dieupon the materials compressing the same into cake formation. Since theplatinum gro-up metal is compressed, the iron powder is forced into thesocket 23 of the lower die and therefore in the finished cake thecompressed iron will have a form juxtaposed to the arc-striking portionwhich is slightly higher :than the surrounding top surface of the spongecathode. After the compression is completed, the cake of materials, withthe embedded wires 20 retained therein, is removed from the dies.

As the compression ofthe materials into ythe socket 23 of the die ten-dsto feather-edge the layer of the platinum group metal arc-strikingportion, it is advisable to machine-off the peripheral por-tion thereofwhile the cake is still green or not set by sintering, land obtain anarc-striking portion which is substantially iiat throughout its entirearea. This will avoid mm tendency during subsequent sintering of cracksor crevices occurring at the edge and spreading to the exposedarc-striking surface. The machining operation may produce a shallowgroove 25 in the surface of the iron body portion without detriment tothe utility of the cathode. The location of wires 20 is sufficientlydistant from the arc-striking area to admit the machine tool used in themachining operation.

Since the materials to be compressed are introduced in powder orgranular condition, the compression thereof will cause someinter-mingling of .the materials at their interfaces and consequentlythere will. not be an absolute demarcation of materials at a deniteplane, but at both sides of a general plane of attachment there will bean interlocking of the two materials. This interlocking of thematerials, in conjunction with the paper-thin characteristic of thearcstriking portion and atomic diffusion during sintering will preventseparation which might otherwise result from different coeflicients ofexpansion.

After the sintering of the compressed cake into an integral mass, atapproximately 1800 F., final steps of fabrication include the placementof the arc-confining ring IB, bending and yattachment of the retainers20 thereto, tting and introduction of the assembly into the ignitron.

While the invention has been described as of particular advantage forcostly materials comprising the arc-striking portion 'and iron as thebody portion, the invention is not necessarily confined to thosematerials as many of the advantages derived `by use of the inventiveconcept apply likewise with employment of other materialsl to constitutethe sponge cathode or parts thereof.

We claim:

1. A sponge cathode comprising Ia body portion of porous material, andan arc-striking portion of a different porous material, saidarc-striking portion being paper-thin and integral with and at thesurface of said body portion.

2. A sponge cathode comprising a body portion of porous material, and anarc-striking portion of a different porous material, said arc-strikingportion being of the order of 0.02 inch in thickness and integral withand at the'surface of said body portion.

3. A sponge cathode comprising a body portion of porous material, and anarc-striking portion of different material integral with and at thesurface of the body portion, said arc-striking portion comprising a thinlayer of a sintered metal of the platinum group.

4. A sponge cathode comprising a body portion of porous material, anarc-striking portion of different material at the surface of and of lessdiameter than said body portion, and an arcconning ring juxtaposed onthe peripheral margin of said arc-striking portion.

5. A sponge cathode comprising a body portion of porous material, anarc-striking portion of different material at the surface of and of lessdiameter than said body portion, an arc-confining ring juxtaposed on theperipheral margin of said arc-striking portion, and retainers projectingfrom said body portion to said arc-confining ring positioning said ringsubstantially coaxially upon said arc-striking portion.

6. A method of fabrication of a sponge cathode comprising filling asocket in a die surface level full with multitudinous particles of onematerial,

covering the `die surface and filled socket with a greater thickness ofmultitudinous particles of 'a diierent material, and compressing saidmaterials simultaneously thereby integrally forming a layer of thecompressed first mentioned material as part of the surface of thecompressed second mentioned different material.

7. A method of fabrication of a sponge cathode comprising filling asocket in a die surface level full with multitudinous particles of onematerial, covering the die surface and lled socket with a greaterthickness of multitudinous particles of a different material, andcompressing said materials simultaneously thereby integrally forming alayer of the compressed first-mentioned mate- 15 5 mentioned differentmaterial.

GERHARD LEWIN ERNEST A. GGLDMAN.

References Cited in the le of this patent UNITED STATES PATENTS NumberName Date 2,218,386 Smith Oct. 15, 1940 2,468,037 Clark Apr. 26, 1949

